US3384685A - Fluoroaryl phosphate esters - Google Patents

Description

United States Patent Oflice Patented May 21, 1968 ABSTRACT OF THE DISCLOSURE Triaryl phosphates of which the aryl groups include at least one monofluorinated aryl group, useful particularly at elevated temperatures as hydraulic. fluids, lubricants and heat transfer or cooling media, for aircraft systems and for industrial use. Typical preferred compounds include m-fluorophenyl diphenyl phosphate and m-fluorophenyl p-fluorophenyl phenyl phosphate.

This invention relates to certain fluoroaryl phosphate esters and is particularly concerned with the provision of novel fluorinated triaryl phosphates.

It is an object of the present invention to provide a series of compounds having high fire resistance, high temperature stability, and which remain in liquid form over a wide temperature range and are relatively nonvolatile at elevated temperatures.

Another object of the invention is the provision of fluorinated triaryl phosphate esters having the above-noted properties and other advantages, and having particular ,I

utility as hydraulic fluids or components thereof, heat transfer fluids, and as lubricants.

Other objects and advantages will appear hereinafter. We have discovered that the above-noted objects are achieved according to the invention by the provision of a class of fluoroaryl phosphates having the formula where R is a member selected from the group consisting of monofluorophenyl, monofluorocresyl and monofluoroxylyl, and R and R" are each a member selected from the group consisting of phenyl, cresyl, xylyl, monofluorophenyl, monofluorocresyl and monofluoroxylyl. R and R can be the same or different.

The fluorine substituent can be carried in ortho, meta or para position on the phenyl, cresyl or xylyl nucleus, with respect to the attachment of such nucleus to the oxygen atom of the phosphate ester. However, the meta fluoro derivatives generally are preferred because such meta fluoroaryl phosphate esters according to the invention have a wider liquid range and a lower melting point as compared to the corresponding para and ortho derivatives.

According to the above general formula and as will be apparent further hereinafter, the fluorinated triaryl phosphate esters of the invention can include esters having only one fluoroaryl, e.g., fluorophenyl, group, two fluoroaryl groups or three fluoroaryl groups. Compounds which contain fluorophenyl groups are preferred over those containing fluorocresyl or fluoroxylyl groups. Where the phosphate esters of the invention contain cresyl or xylyl groups, it is preferred that the ester also contain at least one phenyl group. The preferred esters further are those which contain fluorophenyl groups as compared to those containing fluorocresyl or fluoroxylyl groups. Thus, where the ester contains phenyl, and also cresyl and/or xylyl groups, it is preferred that at least the phenyl group be monofluorinated.

The preferred triaryl phosphate esters of the invention are the monofluorophenyl diphenyl phosphates, the his- (monofluorophenyDphenyl phosphates, and the tris- (monofluoro-phenyl)phosphates. Such compounds have the general formula where X is a member selected from the group consisting of hydrogen and fluorine, there being at least one fluorine atom in the molecule and said fluorine atom or atoms preferably being in meta position in the phenyl nuclei.

It has been found that the above-defined fluoroaryl phosphates are particularly valuable as functional fluids, e.g., as base stocks for hydraulic fluids, and are also useful as heat transfer media and as lubricants due to the advantageous physical properties of such compounds. These properties include high fire resistance, increased temperature stability, and liquidity over a relatively wide temperature range. Thus, for example, generally these fluorinated phosphate esters have a thermal stability in the range of about 600- to about 800 F., autoignition temperatures of the order of about 900 to about 1,000 F. and remain liquid down to a temperature of the order of about 60 F. Further, the viscosity of such fluoroaryl phosphate esters at low temperatures of the order of -25 to 40 F. permits the operative use of such liquids as hydraulic fluids, cooling media and lubricants in these low temperature ranges. These compounds are also relatively nonvolatile at elevated temperatures due to the high boiling point of these materials. Also, certain of the phosphate esters of the invention, particularly the metafluorophenyl phosphate derivatives, have relatively low pour points, e.g., of the order of F. to F. or lower, which together with the relatively low viscosity of these materials at low temperatures, permit the liquid compounds to be pumped without high expenditure of energy at low temperatures. Moreover, the phosphate esters of the invention have good hydrolytic stability, and do not adversely affect materials, such as metals, e.g., steel, aluminum, and the like, with which they may be in contact.

The above-noted properties render many of the fluoroaryl phosphate esters hereof, and especially the metafluorophenyl derivatives, particularly useful as hydraulic fluids, lubricants and heat transfer media, e.g., cooling fluids, in aircraft systems, especially modern high-speed aircraft systems.

Those fiuoroaryl phosphate esters of the invention having pour points and melting points above 0 F., for example those containing ortho fluoro and/ or para fluoro substituents, can be employed as general industrial hydraulic fluids and lubricants particularly where high fire resistance and high thermal stability are important characteristics, e.g., in high pressure systems, such as hydro electric turbines, air compressors and hydraulic presses having various sources of ignition which would result in fire and explosion from leaking hydraulic fluids in the event such fluids are not adequately fire resistant.

Also, the above-noted relatively higher melting derivatives, and including, for example, the o-cresyl substituted phosphate esters according to the invention, can

3 be employed as additives in combination with compatible phosphate esters such as the m-fluorophenyl phosphate esters hereof, or other phosphate esters such as the fluorinated diaryl phosphate esters of the copending application Ser. No. 364,763 filed May 4, 1964, of Seil et al. now Patent No. 3,308,207, to function as thickeners, lubricity improvers or pour point depressants for such esters, e.g., when the latter are employed as hydraulic fluid base stocks. When so employed as additives, the compounds of the invention are used generally in a proportion of about 1 to about 10% by weight of the total composition.

The fluoroaryl phosphate esters of the invention can be produced by reacting a suitable phenol or monofluorophenol compound, or mixtures thereof, with a suitable aryl, e.-g., phenyl or monofluorophenyl, phosphoryl dichloride, or with a suitable diaryl, e.g., diphenyl or bis (fluorophenyl) phosphoryl chloride, preferably in the presence of pyridine or any other suitable HCl acceptor. The proportion of HCl acceptor or pyridine generally employed is usually about equimolar with respect to the phenol compound employed. Where, for example, a phenyl or fluorophenyl phosphoryl dichloride is used, a proportion of about 2 moles of the phenol compound to one mole of the phosphoryl dichloride is employed. Where, for example, a diphenyl or bis (fluorophenyl) phosphoryl chloride is used, a proportion of about one mole of the phenol compound to one mole of the phosphoryl chloride is utilized. Monofiuorophenyl phosphoryl dichloride and bis(monofiuorophenyl) phosphoryl chloride are the subject of the invention of the copending application Ser. No. 421,641. filed of even date herewith, of Robert H. Boscnan and James P. Holder, and the method of preparation of these compounds is described in said application.

The tris(monofiuoroaryl), e.g., tris(monofiuorophenyi), phosphate esters of the invention are prepared by reacting a suitable monofluorophenol compound with phosphorus oxychloride in a proportion of about 3 moles of the fluorophenol to one mole of POCl The reaction is carried out generally by heating the reaction mixture, which may also include an organic solvent, e.g., benzene, for a period of time, e.g., several hours, removing the organic phase containing the phosphate ester reaction product, preferably washing, and then drying such organic material, and distilling this material, usually at low pressure, to separate the phosphate ester present from excess phenol compound, and to remove water and any organic solvent present.

Specific examples of fiuoroaryl phosphates of the invention are as follows:

if l Q I? @WQ) l C C t Q O l (11) F CH3 fil l c z (14) F CH3 l? WG C113 (15) F CH3 CH (10) CH3 F Some of the preferred compounds of the invention are compounds (1) to (5) above. Compound (1) especially possesses a combination of viscosity characteristics, pour point, liquid range, thermal stability, and lubricity, rendering such compound particularly valuable as a hydraulic fluid, lubricant and cooling medium, and as especially suitable for use in hydraulic systems of aircraft.

The following are examples of preparation and use of the compounds of the invention:

Example 1.-Bis(m-fluorophenyl) phenyl phosphate To a mixture of 117.7 g. (1.05 moles) of m-fiuorophenol, 87.0 g. (1.10 moles) of pyridine and 400 ml. of benzene was added dropwise with stirring 105.5 g. (0.500 mole) of re-distilled phenylphosphoryl dichloride. The temperature was maintained at 15-20 C. during the addition, which was complete in 2 hours. The mixture was heated to reflux temperature and refluxed overnight. The mixture was then cooled and poured into 700 ml. of

water. The bottom aqueous layer was withdrawn from the upper organic layer and was extracted with three 125 ml. portions of ether. The ether extracts were added to the organic layer, which was then washed with successive 100 ml. portions of 5% hydrochloric acid and 5% sodium bicarbonate, then washed with three 60 ml. portions 'of water. After drying over anhydrous magnesium sulfate, the solvents were removed by evaporation on a steam bath.

The residue was distilled at reduced pressure; the main phosphate esther fraction, 147.1 g. (81.2% yield) distilled at 159-160 C. (0.12 mm. mercury).

Analysis-Calculated for C H F O P: C, 59.68; H, 3.62; F, 10.49; P, 8.55. Found: C, 59.85; H, 3.64; F, 9.90; P, 8.49.

The resulting phosphate ester product, compound (1) above, has a density of 1.325 g./ml. at 77 F., a kinematic viscosity at F. of 416 centistokes, and a pour point of -60 F. The compound remains liquid over a broad temperature range. In addition, such phosphate has a thermal stability up to 753 F., high autoignition temperature, good hydrolytic stability, and high fire resistance.

A Shell 4-ball wear test on the phosphate ester of this example, carried out at 1,200 r.p.m. for 1 hour at 400 F. using a 40 kgm. load for steel on steel, gave a scar diameter of 0.70 mm., indicating that such phosphate ester has excellent wear properties and excellent lubricity.

An oxidation corrosion test of the phosphate ester of this example on various metals was carried out by contacting such ester with the respective metals at 550 F. for 24 hours. The results are noted below in Table I.

TABLE 1 Metal: Corrosion mg./cm. Aluminum +0.02 Steel --0.01 Silver +0.06 Titanium +0.08

Example 2.Tris (m-fluorophenyl) phosphate To a mixture of 24.7 g. (0.221 mole) of m-fluorophenol, 18.3 g. (0.231 mole) of pyridine and 35 ml. of benzene was added dropwise with stirring 10.7 g. (0.070 mols) of redistilled phosphorus oxychloride. The temperature was maintained at 15 -25 C. during the addition, which was complete in 45 minutes. The mixture was heated to reflux temperature and refluxed for 22 hours.

The mixture was then cooled and poured into 250 ml. of water. The lower organic layer was withdrawn and the aqueous layer was extracted with three 50 ml. portions of ether. The ether extracts were added to the organic layer, which was then washed with successive 25 ml. portions of 5% hydrochloric acid, 5% sodium bicarbonate, and water. After drying over anhydrous magnesium sulfate, the solvents were removed by heating on a steam bath. The residue Was the distilled at reduced pressure, and the main product fraction, 20.3 g. (76.2% yield) distilled at 176-179 C. (1 mm. mercury).

AnaIysis.Calculated: C, 58.86; H, 3.18; P, 8.15. Found: C, 57.90; H, 3.33; P, 7.90.

The resulting product, consisting essentially of tris(mfluorophenyl) phosphate, compound (2) above, has a pour point below about 60 F., has good thermal stability between about 600 and about 800 F., high autoignition temperature in the range of about 900 to about 1,000 F., good hydrolytic stability and high fire resistance. Such phosphate has a wide liquid range and is useful as a base stock component for a hydraulic fluid of an aircraft system and as a lubricant.

Example 3.-m-fluorophenyl p-fluorophenyl phenyl phosphate To a mixture of 35.3 g. (0.315 mole) of m-fluorophenol, 35.3 g. (0.315 mole) of p-fluorophenol, 52.2 g. (0.660 mole) of pyridine and 250 ml. of benzene was added dropwise with stirring 63.3 g. (0.300 mole) of phenyl phosphoryl dichloride. The temperature was maintained at 1015 C. during the addition, which was complete in one hour and 15 minutes. The mixture was heated slowly to reflux temperature and refluxed for 18 hours.

The mixture was then cooled and poured into 400 ml. of water. The lower aqueous layer was withdrawn and extracted with two ml. portions and one 50 ml. portion of ether. The ether extracts were added to the organic layer which was then washed with 100 ml. of 5% hydrochloric acid, 100 ml. 5% sodium bicarbonate and one 100 ml. portion and two 50 ml. portions of water. After drying over anhydrous magnesium sulfate, the solvents were removed by heating on a steam bath. The residue was then distilled at reduced pressure. The main product fraction, 95.4 g. (87.7% yield) distilled at l68169 C. (0.25 mm. mercury).

The product consisting essentially of compound (3) above, m-fluorophenyl p-fluoro'phenyl phenyl phosphate, has a pour point of 50 F., a kinematic viscosity at 0 F. of 744 centistokes, good thermal stability, high autoignition temperature, good hydrolytic stability, and high fire resistance. Such phosphate, having a wide liquid range, is useful as a base stock for a hydraulic fluid of an aircraft system.

Example 4.m-fluorophenyl diphenyl phosphate To a mixture of 62.1 g. (0.660 mole) of phenol, 52.2 g. (0.660 mole) of pyridine and 250 ml. of benzene was added dropwise with stirring 68.7 g. (0.300 mole) of m-fluorophenyl phosphoryl dichloride. The temperature was maintained at 10-17 C. during the addition, which was complete in one hour and 45 minutes. The mixture was heated slowly to reflux temperature and refluxed for 35 hours.

The mixture was then cooled and poured into 500 ml. of water. The upper organic layer was withdrawn and the aqueous layer was extracted with three 100 ml. portions of ether. The ether extracts were added to the organic layer, which was then washed with 100 ml. of 5% hydrochloric acid, 100 ml. of 5% sodium bicarbonate, and three 50 ml. portions of water. After drying over anhydrous magnesium sulfate, the solvents were removed by heating on a steam bath. The residue was then distilled at reduced pressure. The main product fraction, 92.5 g. (89.3% yield) distilled at 168-170 C. (0.19-0.23 mm. mercury).

Analysis.-Calculated for C H FPO C, 62.80; H, 4.10; F, 5.52; P, 9.00. Found: C, 62.88; H, 4.09; F, 5.29; P, 8.90.

The resulting product consisting essentially of compound (4) above, m-fluorophenyl diphenyl phosphate, has a viscosity at 100 F. of 11.4 centistokes, a pour point of about 10 F., a thermal stability up to about 692 F., high autoignition temperature, good hydrolytic stability and high fire resistance. Such phosphate ester is useful as a fire resistant thermally stable hydraulic fluid 0r lubricant for general industrial purposes, e.g., in a hydraulic press or as a compressor lubricant.

Example 5.Bis (p-fluorophenyl)'phenyl phosphate To a mixture of 70.6 g. (0.630 mole) of p-fluorophenol plete in one hour. The mixture was heated slowly to reflux and refluxed for 17 /2 hours.

The mixture was then cooled and poured into 400 ml. of water. The lower aqueous layer was withdrawn and extracted with three 100 ml. portions of ether. The ether extracts were added to the organic layer, which was then washed with 100 ml. of 5% hydrochloric acid, 100 ml. of 5% sodium bicarbonate, and three 50 ml. portions of water. After drying over anhydrous magnesium sulfate, the solvents were removed by heating on a steam bath. The residue was then distilled at reduced pressure. The main product fraction, 95.3 g. (87.7% yield), distilled at 178l80 C. (0.22-0.26 mm. mercury).

AIzaIysis.Calculated for C H F O P: C, 59.68; H, 3.62; P, 8.55. Found: C, 59.56; H, 3.64; P, 8.23.

The product produced, consisting essentially of compound (5) above, bis(p-fluorophenyl) phenyl phosphate, has a melting point of about 40 (1., good thermal stability, high autoignition temperature, good hydrolytic stability, and high fire resistance. Such phosphate is useful as a base stock for a hydraulic fluid or as a lubricant in systems operating at elevated temperatures above about 110 F.

Table 11 below shOWs a comparison of some of the physical properties of the phosphate esters of the inven tion, compounds (1) to (5), produced in Examples 1 to 5 above.

containing at least one m-phenyl group in the triaryl phosphate ester, generally have low pour points, noting particularly compounds (1) to (3) of the table, and that such compounds have relatively low viscosity at F. and below, rendering such compounds useful as hydraulic fluids, lubricants and cooling media at temperatures below 0 F., as previously noted, as well as at elevated temperatures of the order of about 600 to about 800 F., due to their high thermal stability. Of particular significance, it is noted that compound (3) having one m-fluorophenyl and one p-fiuorophenyl group has a low pour point, as compared to compound wherein the mfluorohenyl group of compound (3) is replaced by an additional p-fluorophenyl group, and which has a high melting point. This clearly indicates the influence of the preferred m-fluoroa-ryl e.g., m-fluorophenyl, group in the triaryl phosphate esters of the invention.

Example 6.Bis(m-fiuorophenyl) p-fluorophenyl phosphate The procedure of Example 1 is substantially repeated, employing in place of phenyl phosphoryl dichloride the same molar proportion of p-fluorophenyl phosphoryl dichloride, to thereby obtain compound ('6) above as product, bis (m-fluorophenyl) p-fluorophenyl phosphate.

Example 7.Bis(m-fluorophenyl) m-cresyl phosphate The procedure of Example 1 is substantially repeated, except employing in place of the phenyl phosphoryl dichloride the same molar proportion of meta cresyl phosphoryl dichloride. The product obtained is compound (11) above, bis(m-fluoropheny-l) m-cresyl phosphate.

Example 8 A mixture is prepared consisting of 90% by weight of compound (4), m-fluorophenyl diphenyl phosphate,

and 10% by weight of compound (5), bis(p-flourophenyl) phenyl phosphate.

The resulting mixture has improved liquid range as compared to either component of such mixture.

Such mixture is effective as a hydraulic fluid and lubricant in aircraft systems.

Example 9 A mixture is prepared consisting of by weight of 1,1,5-trihy'droperfluoropentyl diphenyl phosphate and 5% by weight of bis(p-fluorophenyl) phenyl phosphate. The diphenyl phosphate ester above is described in the above copending application. The resulting mixture has improved lubricity and lower pour point as compared to the above diphenyl phosphate ester alone, and is useful as a hydraulic fluid of an aircraft system.

From the foregoing, it is seen that the invention provides a novel class of fluoroaryl, e.g., fluorophenyl, phosphates which are designed particularly for use as base stocks or base stock components or additives of hydraulic fluids, lubricants and heat transfer or cooling media, for aircraft systems and for industrial use.

While we have described particular embodiment of our invention for the purpose of illustration, it should e understood that various modifications and adaptations thereof may be made within the spirit of the invention, as set forth in the appended claims.

We claim: 1. A phosphate ester having the formula ll/ ROP where R is a member selected from the group consisting of monofluorophenyl, monofluorocresyl and monofluoroxylyl, and R and R are each a member selected from the group consisting of phenyl, cresyl, xylyl, monofluorophenyl, monofluorocresyl and monofluoroxylyl.

2. A phosphate ester as defined in claim 1, wherein at least one of said groups R and R" is monofluorophenyl.

3. A phosphate ester as defined in claim 1, wherein at least one of said groups R and R" is phenyl.

4. A phosphate ester as defined in claim 1, wherein at least one of said groups R and R is cresyl.

5. A phosphate ester as defined in claim 1, wherein R is monofluorophenyl and R and R are each phenyl.

6. A phosphate ester as defined in claim 1, wherein R is monofluorophenyl, R is monofluorophenyl and R is phenyl.

7. A phosphate ester as defined in claim 6, wherein at least one of said groups R and R is m-fluorophenyl.

8. A phosphate ester as defined in claim 1, wherein R, R and R are each monofluorophenyl.

9. A phosphate ester as defined in claim 8, wherein at least one of said groups R, R and R" is m-fluorophenyl.

10. A phosphate ester as defined in claim 8, wherein at least two of said groups R, R and R are each mfluorophenyl.

11. Bis(mfluorophenyl)phenyl phosphate.

12. Tris(m-fluorophenyl) phosphate.

13. m-Fluorophenyl p-fiuorophenyl phenyl phosphate.

14. m-Fluorophenyl diphenyl phosphate.

15. Bis(p-fluorophenyl)phenyl phosphate.

References Cited UNITED STATES PATENTS 2,033,916 3/1936 Bass 260-966 2,727,058 1 2/1955 Conly 260950 2,754,316 7/1956 Conly 260955 CHARLES E. PARKER, Primary Examiner.

B. BILLIAN, A. H. SUTTO, Assistant Examiners.